Jon had no idea what to do to fix his hasty wish. No, that wasn't true. He did have one idea. "I wish that when I said girls it means what I'd think of girls as in girls and guys, so young kids and older people don't count."
Okay. If that works it'll stop him from being accused of being a child molester. But it still wasn't enough. There were plenty of girls his age. How could he undo that? It was impossible. No, it couldn't be impossible after all. The problem wasn't girls touching it... well, it was, but the biggest problem was girls touching it and making wishes.
"I wish that girls who touch my penis can't make wishes on it."
Which was the wrong thing to say. The original wish, that Jon didn't hear, was that Jon gets wishes by touching it and other people get wishes by touching it flesh to flesh.
Anyone who touches it flesh to flesh gets to make a wish. But Jon just wished that girls who touch it don't get to make a wish. There was only one way for the second wish to happen without reversing the first. Abruptly, Jon felt a tugging at his groin and his penis was stone, and had fallen off his body onto his bed. Since it was no longer flesh, both wishes would be true without contradiction. Anyone who touches it flesh to flesh makes a wish, but that would be nobody.
At least Jon himself could get wishes by touching it, since he didn't have to do so flesh to flesh. But could he ever figure this out? And how could he get a penis made of flesh again without contradicting one of the two earlier wishes that almost contradicted themselves?